An automatic sprinkler system is one of the most widely used devices for fire protection. These systems have sprinklers that are activated once the ambient temperature in an environment, such as a room or a building, exceeds a predetermined value. Once activated, the sprinklers distribute fire-extinguishing fluid, preferably water, in the room or building. A sprinkler system, depending on its specified configuration is considered effective if it controls or suppresses a fire. Failures of such systems may occur when the system has been rendered inoperative during building alteration or disuse, or the occupancy hazard has been increased beyond initial system capability.
The sprinkler system can be provided with a suitable fire fighting fluid or a water supply (e.g., a reservoir or from a municipal water supply). Such supply may be separate from that used by a fire department. Regardless of the type of supply, the sprinkler system is provided with a main that enters the building to supply a riser. Connected at the riser are valves, meters, and, preferably, an alarm to sound when water flow within the system is above or below a predetermined minimum value. At the top of a vertical riser, a horizontally disposed array of pipes extends throughout the fire compartment in the building. Other risers may feed distribution networks to systems in adjacent fire compartments. Compartmentalization can divide a large building horizontally, on a single floor, and vertically, floor to floor. Thus, several sprinkler systems may serve one building.
In a piping distribution network, branch lines carry the sprinklers. A sprinkler may extend up from a branch line, placing the sprinkler relatively close to the ceiling, or a sprinkler can be pendent below the branch line. For use with concealed piping, a flush-mounted pendant sprinkler may extend only slightly below the ceiling.
Various standards exist for the design and installation of a fire protection system. In particular, the National Fire Protection Association (“NFPA”) describes, in its Standard for the Installation of Sprinkler Systems 13 (2002) (“the NFPA 13”) along with Standards 13D and 13R, various design consideration and installation parameters for a fire protection system. NFPA 13, 13D, and 13R recognize the use of residential sprinklers by requiring that such sprinkler in a residential fire protection system to be installed based on certain criteria for residential occupancies, which can include commercial dwelling units (e.g., rental apartments, lodging and rooming houses, board and care facilities, hospitals, motels or hotels).
In order, however, for a residential sprinkler to be approved for installation under NFPA Standards, such sprinkler must pass various tests promulgated by, for example, Underwriters Laboratory Incorporated (“UL”) in its Underwriter's Laboratory Residential fire sprinklers for Fire-Protection Service 1626 (“UL Standard 1626”) in order to be listed for use as a residential sprinkler. Specifically, UL 1626 (October 2003) requires a sprinkler, as described in Table 6.1 of Section 6, to deliver a minimum flow rate (gallons per minute or “GPM”) for a specified coverage area (square feet or “ft2”) to provide for a desired average density of 0.05 GPM/ft2. The minimum flow rate tabulated in Table 6.1 can be used to calculate a predicted minimum fluid pressure needed to operate a sprinkler by virtue of a rated K-factor of the sprinkler. A rated K-factor of a sprinkler provides a coefficient of discharge of the flow passage of the sprinkler, is defined as follow:
                    K        ⁢                  -                ⁢        factor            =              Q                  √          p                      ⁢                  ⁢          where      ⁢                          ⁢      Q      ⁢                                        ⁢                                      ⁢      is      ⁢                          ⁢      the      ⁢                          ⁢      flow      ⁢                          ⁢      rate      ⁢                          ⁢      GPM      ⁢                          ⁢      and        ⁢                  ⁢          p      ⁢                          ⁢      is      ⁢                          ⁢      pounds      ⁢                          ⁢      per      ⁢                          ⁢      square      ⁢                          ⁢      inch      ⁢                          ⁢      gauge        )
In order for a sprinkler to pass actual fluid distribution tests, as described in Sections 26 and 27 of UL 1626, the actual minimum pressure of the sprinkler, however, may not be the same as the predicted minimum pressure, which can be calculated using the given minimum flow rate of Table 6.1 in UL 1626 and the rated K-factor of the sprinkler. Further, the actual minimum fluid flow rate to pass these distribution tests of UL 1626 for a specified coverage area may even be higher than the tabulated minimum flow rate given in Table 6.1 of UL 1626. Consequently, any attempt to provide for a listed sprinkler (i.e., an operational sprinkler suitable for the protection of a dwelling unit) cannot be predicted by applications of a known formula to known residential sprinklers.
Known residential fire sprinklers have been tested to meet these performance qualifications required by UL 1626. When these known sprinklers are designed to be installed in an actual system according to the 2002 Edition of NFPA 13, 13, and 13R (2002) for a large protection area of 324 square feet or greater, however, these existing residential fire sprinklers require a fluid pressure, based on its discharge coefficient or K-factor, that places a greater demand on the fluid pressure source than that predicted by the application of the tabulated minimum flow rate of UL 1626 and the rated K-factor.
For example, a known 4.9 K-factor residential sprinkler can provide the required minimum flow rates of 20 GPM to pass the distribution tests for a 20 feet by 20 feet coverage area whereas another commercially available 4.9 K-factor residential sprinkler by another manufacturer cannot. Another 4.9 K-factor residential sprinkler has satisfied the UL 1626 testing requirements for a 18 feet by 18 feet coverage area with the actual flow rates for these UL 1626 tests being the same as the required minimum flow rates in Table 6.1 of UL 1626 and at a pressure predicted by the 4.9 K-factor value. A known larger K-factor sprinkler of 5.8 K-factor, however, operates at a higher flow rate (19 GPM) than the permitted minimum flow rate (17 GPM) for a coverage area of at least 324 square feet and at a higher pressure (10.8 psi) than a predicted pressure (8.6 psi) based on its K-factor value and permitted minimum flow rate of 17 GPM. Thus, these examples show that there is a great amount of uncertainty in any potential sprinkler design that cannot be determined unless the sprinkler is built and tested in accordance with a testing or listing authority.
Notwithstanding the inability of known sprinklers to operate at the predicted pressure value for a specified coverage area and minimum flow rate required by the listing authority, it would nevertheless be beneficial to provide for a residential sprinkler to achieve a lower pressure demand as compared to existing residential fire sprinklers while meeting the performance requirements of listing authority, such as, for example, the tests set forth in UL 1626 (October 2003), including vertical and horizontal fluid distribution tests. The lower pressure demand of such residential fire sprinkler would allow a fire protection system designer to have greater leeway in residential applications that are installed in accordance with NFPA 13, 13D, and 13R (2002) for a design protection area under the NFPA Standards. Further, the lower pressure demand of such sprinkler would provide a minimum design pressure that will allow such designer to tailor the flow rate requirements demanded by the design protection area to the sprinkler with the best flow rate and pressure for a system installed in accordance with the 2002 Edition of NFPA 13, 13, and 13R.